The splanchnic mesoderm in the cardiogenic region where the heart develops; it gives rise to endocardial heart tubes that fuse to form the primordial cardiac tube, the heart primordium[web]. Two migratory heart primordia that move ventrally during the course of neurulation, and then fuse[XAO]. [ http://www.drugs.com/dict/cardiogenic-mesoderm.html https://github.com/obophenotype/insect_neuroanatomy_ontology/issues/7 ]